The present invention relates to a pneumatic tire, more particularly to a bead structure being capable of improving the bead durability.
In general, a pneumatic tire is provided in each bead portion with a bead core as a tension member. And the carcass is secured to the bead core by folding back its edge around the bead core.
The bead core is usually made of windings of at least one steel wire. In order to bind the windings to improve the handling during tire making processes, sometimes a canvas tape is tightly wound therearound.
On the other hand, as disclosed in U.S. Pat. No. 5,772,811 or European Patent 749855 equivalent thereto, we have proposed a heavy duty tire in which a bead apex rubber disposed immediately radially outside the bead core is minimized, whereas the bead portion of a heavy duty tire is conventionally reinforced with a large volume of bead apex rubber and bead reinforcing layers.
In such tire, therefore, the bead portion is relatively supple and deformation or deflection of the bead portion during running is relatively large. As a result, the carcass tension becomes especially large on the axially inside of the bead core. Therefore, it is very important to prevent the carcass cords from contacting with the bead wire to prevent the carcass cords from being cut. Further, a large sharing stress occurs between the bead apex rubber and the outer face of the bead core. Therefore, it is important to prevent the bead apex rubber from separating from the bead core by mitigating the sharing stress and/or improving the resistance to sharing stress.
If the bead core with a canvas tape is used in such tire, the carcass cords can be prevented from contacting with the bead wire for the moment, but the canvas is liable to be broken in use. And it can not prevent the separation between the bead apex rubber and the bead core. Thus, it is difficult to improve the durability of the bead portion.
It is therefore, an abject of the present invention to provide a pneumatic tire in which the above-mentioned drawbacks are resolved and the bead durability is effectively improved.
According to the present invention, a pneumatic tire comprises
a pair of bead portions each provided therein with a bead core made of windings of at least one wire,
a carcass ply of cords extending between the bead portions and turned up around the bead core from the axially inside to the outside of the tire to form a pair of turnup portions and a main portion therebetween,
a rubber bead apex disposed radially outside the bead core and between each turnup portion and the main portion,
a fiber reinforced rubber spacer interposed between the bead core and the carcass ply to provide a positive distance between the carcass ply cords and bead core wire,
the fiber reinforced rubber spacer having a securing portion which extends radially outwardly and axially outwardly from the axially inside of the bead core while separating from the bead core but contacting with the rubber bead apex, and
a distance (L1, L2) between an outermost point of the securing portion and the bead core being in a range of from 0.05 to 1.0 times a height of the bead core.